I have never heard of a graphics card dieing because of a graphically intense game. I supose, theoretically, if a game is so graphically intense, and your video card is overclocked to the max, working at max capacity, it could overheat and fry the GPU. However, several things would have to happen...
1. You would have had to OC your card
2. Your game would have to be ungodly detailed
3. You would have to have a passive cooling system, perhaps no cooling system at all.
even then, almost all video cards simply shut off when they heat up past a certian point
To give it to you short, there is a 1 in 1 billion chance it could maybe happen to someone someday perhaps if venus, jupiter, and pluto are alligned and the tides are exactly 4" above low tide, as a thuder storm passes overhead

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I hightly doubt that it could happen. You may expierence a drop in FPS, but you wont fry a video card. Your expierence was most likely coincidence.